This invention relates to a control device for hydraulic brake systems including wheel locking regulation apparatus. The device has a piston which is tightly slidable in a bore. The piston on one side thereof defines an inlet chamber connected with a main cylinder and on the other side an outlet chamber which is connected with at least one wheel cylinder. The piston has a passage closable by a valve member which connects the inlet chamber with the outlet chamber. The valve member in the final position of the piston, in which the outlet chamber has its smallest volume, is mechanically held open. The piston is movable in the bore by means of a control piston defining a control chamber for the purpose of enlarging the outlet chamber and a reaction piston designed as a differential piston defines the inlet chamber, wherein the smaller application surface of the reaction piston faces the inlet chamber and the larger application surface defines a reaction chamber which is directly connected to a hydraulic accumulator.
Such a device is already known from German Patent No. DE-OS 26 44 659. This device eliminates or at least substantially reduces shocks at the brake pedal which occurred with formerly customary arrangements during the wheel locking regulation cycle. Disadvantages of this device include a complicated construction which increases its cost and a large amount of auxiliary energy is required.